Identification

Title

Influences of environmental relative humidity and horizontal scale of subcloud ascent on deep convective initiation

Abstract

This study examines two factors impacting initiation of moist deep convection: free-tropospheric environmental relative humidity (phi(E)) and horizontal scale of subcloud ascent (R-sub), the latter exerting a dominant control on cumulus cloud width. A simple theoretical model is used to formulate a "scale selection" hypothesis: that a minimum R-sub is required for moist convection to go deep, and that this minimum scale decreases with increasing phi(E). Specifically, the ratio of R-sub(2) to saturation deficit (1 - phi(E)) must exceed a certain threshold value that depends on cloud-layer environmental lapse rate. Idealized, large-eddy simulations of moist convection forced by horizontally varying surface fluxes show strong sensitivity of maximum cumulus height to both phi(E) and R-sub consistent with the hypothesis. Increasing R-sub by only 300-400 m can lead to a large increase (>5 km) in cloud height. A passive tracer analysis shows that the bulk fractional entrainment rate decreases rapidly with R-sub but depends little on phi(E). However, buoyancy dilution increases as either R-sub or phi(E) decreases; buoyancy above the level of free convection is rapidly depleted in dry environments when R-sub is small. While deep convective initiation occurs with an increase in relative humidity of the near environment from moistening by earlier convection, the importance of this moisture preconditioning is inconclusive as it is accompanied by an increase in R-sub. Overall, it is concluded that small changes to R-sub driven by external forcing or by convection itself could be a dominant regulator of deep convective initiation.

Resource type

document

Resource locator

Unique resource identifier

code

http://n2t.net/ark:/85065/d72v2kvc

codeSpace

Dataset language

eng

Spatial reference system

code identifying the spatial reference system

Classification of spatial data and services

Topic category

geoscientificInformation

Keywords

Keyword set

keyword value

Text

originating controlled vocabulary

title

Resource Type

reference date

date type

publication

effective date

2016-01-01T00:00:00Z

Geographic location

West bounding longitude

East bounding longitude

North bounding latitude

South bounding latitude

Temporal reference

Temporal extent

Begin position

End position

Dataset reference date

date type

publication

effective date

2022-02-01T00:00:00Z

Frequency of update

Quality and validity

Lineage

Conformity

Data format

name of format

version of format

Constraints related to access and use

Constraint set

Use constraints

Limitations on public access

None

Responsible organisations

Responsible party

contact position

OpenSky Support

organisation name

UCAR/NCAR - Library

full postal address

PO Box 3000

Boulder

80307-3000

email address

opensky@ucar.edu

web address

http://opensky.ucar.edu/

name: homepage

responsible party role

pointOfContact

Metadata on metadata

Metadata point of contact